1. Filed of the Invention
This invention relates to a digital indication type measuring machine.
2. Description of the Prior Art
In general, a so-called digital indication type measuring machine, wherein a measuring machine such as a micrometer, slide calipers or the like attachingly provided with an encoder and a measured value is digitally indicated, has been widely utilized because of such advantages that the reading of a measured value is easily performed and the measuring accuracy is high. Out of such digital indication type measuring machines, as a measuring machine for measuring an inner diameter of a work, there has been known a so-called a hole tester (inner diameter measuring instrument), in which three measuring elements arranged at intervals of 120.degree. for example, are simultaneously enlarged in diameter and an inner diameter is measured by projection values of the measuring elements.
In the hole tester of the type described, a spindle, a dial gauge and the like are generally provided in a direction perpendicular to the direction of enlarging the diameter of the measuring elements so that the hole tester can be applied to a deep hole and the like. In this case, as the means for converting a displacement of the spindle to displacements of the measuring elements, a tapered surface, a cam, a link mechanism and the like are used in many cases. However, in order to achieve high controllability and high precision measurement, it is necessary that the main body be rendered compact in size and have a small diameter. Hence, the range of measurement covered by one hole tester is very limited. In consequence, as far as the hole tester is concerned, a plurality of hole testers different in size for every ranges of measurement should be prepared, thus resulting in an increased economic burden.
In contrast thereto, there has been known such a hole tester, in which only the displacement converting mechanism and measuring elements are replaced with new ones with the main body remaining the same, so that the measuring range can be enlarged. However, the hole tester of this type requires the matching between the measuring diameter and the dial graduation or thimble graduation. Hence, the finishing accuracies of the main body and the members on the converting side and the method of fixation therebetween become strict, thus resulting in increased manufacturing costs and inconvenience in handling. Furthermore, the adjustment between the position of the spindle and the graduation for the absolute calibration is required for each replacement, thus resulting in decreased working efficiency.
Now, with the development in the electronic technology, the measuring machines of recent type has been provided with the functions such as zero point setting, change-over between inch and mm and the like, which have not been provided with the conventional measuring instruments. However, if the main body of the measuring machine would become large in size along with such a development as described above, the value of the development would be reduced to a considerable extent.
Here, from an antinomy between an increased function and a device compact in size leads to questions concerning the sizes and locations of control switches in particular. More specifically, since the control switches should be as small as possible and should be disposed at a specific surface of a measuring instrument, there is presented such a problem that an unaimed switches tend to be mistakenly operated.
This is particularly true with the aforesaid hole tester and the like, whereby a blind operation is required because the measurement should be completed in a hole and the reading should be performed outside the hole. Furthermore, in a measuring instrument with means of high-class functions, wherein a plurality of functions are provided in a single switch in order to reduce an absolute number of switches, to thereby achieve the program switching and the like, there is presented the disadvantage that a measurer cannot grasp the meaning of the contents of indication.